A composite additive for preparing high-silicon silicon-manganese alloy and a preparation method thereof

Abstract

This application provides a composite additive for preparing high-silicon manganese alloys. The additive has a spherical particle structure and comprises, from the inside out, a core layer, a transition layer, and an outer shell layer. The mass percentages of each layer are as follows: core layer 35%–45%, transition layer 30%–40%, and outer shell layer 20%–30%. The outer shell layer is composed of the following components in the indicated mass percentages: calcium carbonate 50%–60%, red mud 20%–30%, modified bentonite 10%–20%, and silica powder 3%–7%. The transition layer is composed of the following components in the indicated mass percentages: fluorite powder 30%–40%, dolomite 20%–30%, borax 10%–20%, blast furnace slag 15%–25%, and silica powder 3%–7%. The core layer is composed of the following components in the indicated mass percentages: activated coke 65%–75%, manganese ore powder 15%–25%, and silicon carbide 8%–12%. This application also provides a method for preparing the composite additive and a method for using it.

Description

Technical Field

[0001] This application relates to the field of special alloy preparation, and in particular to a composite additive for the preparation of high silicon manganese alloys and its preparation method. Background Technology

[0002] High-silicon ferromanganese alloys, used as intermediate raw materials in the production of low-carbon ferromanganese, metallic manganese, and special steels, rely on high-temperature reduction reactions above 1600℃ in submerged arc furnaces for smelting. This process demands high levels of permeability of the furnace charge, temperature distribution, and reaction stability. When problems arise with furnace charge permeability or gas production, sparking can easily occur. Sparking is the sudden ejection of high-pressure, high-temperature gas from weak points in the charge layer. Sparking not only causes additional loss of reducing agent but also leads to insufficient electrode insertion depth, resulting in increased power consumption per ton of product. In severe cases, it can even cause safety accidents such as burns to personnel and equipment damage. Common causes of sparking include: Ingredient issue: Improper ratio of reducing agent (too much or too little) leads to poor permeability of the furnace charge; Improper operation: uneven feeding, untimely furnace tamping, unreasonable material surface shape, and gas cannot be discharged evenly from the furnace; Electrode abnormality: The working end of the electrode is too short or the insertion depth is insufficient, the heat is concentrated on the surface of the furnace charge, or the electrode surface is adhered with impurities such as silicon carbide.

[0003] Traditional methods of controlling fire ignition primarily rely on emergency operations such as manually puncturing the furnace charge and tamping the furnace. While these methods can temporarily clear gas channels, the effects are short-lived, and frequent operations can disrupt the descent sequence of the furnace charge, leading to greater fluctuations in product composition. Existing technologies often mitigate fire ignition by optimizing the particle size distribution of raw materials and adjusting slag alkalinity. However, fire ignition problems caused by poor furnace charge permeability due to improper batching or operation remain prevalent. Summary of the Invention

[0004] In view of this, this application proposes a composite additive for the preparation of high silicon manganese alloy that can improve the permeability of furnace charge. The composite additive has a coating structure and improves the permeability of furnace charge through chemical or physical changes that occur during heating, thereby reducing the problem of sparking.

[0005] This application also proposes a method for preparing a composite additive.

[0006] This application also proposes a method for using a compound additive.

[0007] A composite additive for preparing high-silicon manganese alloys has a spherical particle structure, comprising a core layer, a transition layer, and an outer shell layer from the inside out, with the following mass percentages for each layer: core layer 35%–45%, transition layer 30%–40%, and outer shell layer 20%–30%. The outer shell layer is composed of the following components in the indicated mass percentages: 50%–60% calcium carbonate, 20%–30% red mud, 10%–20% modified bentonite, and 3%–7% silica fume. The transition layer is composed of the following components in the indicated mass percentages: fluorite powder 30%–40%, dolomite 20%–30%, borax 10%–20%, blast furnace slag 15%–25%, and silica fume 3%–7%. The core layer is composed of the following components by mass percentage: 65%–75% activated coke, 15%–25% manganese ore powder, and 8%–12% silicon carbide.

[0008] A method for preparing a composite additive includes the following steps: The core layer raw materials are mixed evenly according to the formula, a binder is added, and the core particles are formed into 5-8 mm core particles by a disc granulator and then dried. A bottom-spray fluidized bed is used to coat the core particles with a transition layer. First, the transition layer powder is sprayed, and then the binder is atomized and sprayed in to coat the particles until the particle size is 8-15 mm. Lower the fluidized bed temperature, coat the outer shell layer in the same way as the previous step, until the final particle size is 10-19 mm, and then dry and solidify.

[0009] A method of using the above-mentioned three-layer coated additive includes the following steps: Weigh out 2% to 3% of the total mass of the charge in the electric arc furnace and add it to the mixer at the same time as the main materials of manganese ore, silica, coke, and flux. The mixed furnace charge is added to the electric arc furnace using a ring or multi-point feeding method; Adjust the proportion of composite additives according to the furnace conditions.

[0010] The technical advantages of this application are as follows: The outer shell layer corresponds to the preheating zone of the upper layer of the furnace charge. In this zone, the outer shell layer completely decomposes, creating pores for ventilation and preventing crust formation on the upper layer of the furnace charge. The transition layer corresponds to the softening zone of the middle layer of the furnace charge. In this zone, the transition layer completely melts, reducing slag viscosity and improving slag fluidity, allowing the slag to flow downwards in a timely manner and preventing slag from clogging the airflow channels in the softening zone. The core layer corresponds to the main reaction zone above the molten pool. The main component of the core layer is a reducing agent, which can stabilize the reaction rate, reduce the formation of silicon carbide hard shells, and maintain a stable gas production rate in the main reaction zone for a long time, thereby stabilizing the furnace pressure. Throughout the process, the composite additive moves downwards synchronously with the furnace charge and plays a role in the corresponding zone under the influence of temperature rise, significantly improving the problem of sparking. Detailed Implementation

[0011] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0012] A composite additive for preparing high-silicon manganese alloys has a spherical particle structure, comprising a core layer, a transition layer, and an outer shell layer from the inside out, with the following mass percentages for each layer: core layer 35%–45%, transition layer 30%–40%, and outer shell layer 20%–30%. The outer shell layer is composed of the following components in the indicated mass percentages: 50%–60% calcium carbonate, 20%–30% red mud, 10%–20% modified bentonite, and 3%–7% silica fume. The transition layer is composed of the following components in the indicated mass percentages: fluorite powder 30%–40%, dolomite 20%–30%, borax 10%–20%, blast furnace slag 15%–25%, and silica fume 3%–7%. The core layer is composed of the following components by mass percentage: 65%–75% activated coke, 15%–25% manganese ore powder, and 8%–12% silicon carbide.

[0013] Within the core layer, the activated coke exhibits well-developed pores, providing abundant adhesion sites for manganese ore powder and silicon carbide, resulting in more uniform mixing of the components. The manganese ore powder used is high-manganese ore powder of the same grade as the main furnace charge. When uniformly mixed with the activated coke, it preferentially undergoes a reduction reaction at high temperatures. This endothermic reaction suppresses temperature fluctuations caused by concentrated reactions in the main furnace charge. The activated coke can react with the manganese ore powder and silica in advance, thereby releasing CO gas earlier and suppressing gas production fluctuations.

[0014] In a preferred embodiment, the red mud in the outer shell layer is calcined at 280–320°C, with a free alkali content ≤0.5% and a pH value ≤9.

[0015] The composition of red mud varies depending on its source. The red mud used in this application is preferably Bayer process red mud. Red mud has a pH value as high as 10-13; the content of free alkalis, such as Na₂O and K₂O, in red mud can reach 5-10%, and it also contains small amounts of harmful components such as fluorides. Direct use can easily lead to problems such as efflorescence and equipment corrosion. This application uses low-temperature calcination pretreatment, which reacts soluble sodium salts in the red mud, such as sodium carbonate and sodium aluminate, with the silica-alumina components to form stable insoluble sodium aluminum silicate, reducing the free alkali content by 60-80% and lowering the pH value to below 9, thus avoiding efflorescence and metal corrosion problems in subsequent applications. Simultaneously, calcination removes adsorbed fluorides, ammonium salts, and other volatile impurities from the red mud.

[0016] In a preferred embodiment, the modified bentonite is prepared by the following method.

[0017] Add 3-5% Na₂CO₃ to the bentonite slurry, stir and react at 60-80℃ for 30-60 minutes, then use Na… + Ca substitution between layers 2+ Mg 2+ Divalent cations; Sodium-modified bentonite was aged at 80–100℃ under closed hydrothermal conditions for 12–24 hours to allow the Na+ to dissolve. + Completely integrated into the interlayer lattice, the crystal structure becomes more ordered, and the interlayer bonding force is strengthened. First, preheat at 200–220℃ for 1–2 hours to remove free water and some weakly bound water, while retaining hydration and expansion properties; then raise the temperature to 400–450℃ and calcine for 2–3 hours to remove some interlayer bound water, while simultaneously forming a uniform microporous structure inside. Adding 0.5-1% of silane coupling agents, such as KH550 and KH560, modifies the surface of bentonite, enhances its interfacial bonding with polar particles such as manganese ore powder and coke, and further improves particle strength.

[0018] The composite additives of this application are added to the electric arc furnace along with the furnace charge.

[0019] As the furnace charge is heated, when the temperature reaches 400-500℃, the modified bentonite first loses its water of crystallization and expands in volume by 3-4 times, opening up the initial micropores in the gaps between the surrounding furnace charge; the silica powder is uniformly attached to the surface of the furnace charge particles, forming an isolation film to prevent the fine particles from agglomerating and sticking together. When the temperature reaches 500-700℃, the bound water and carbonate components in the red mud gradually decompose, releasing H2O and CO2 gases, further expanding the pore channels, and releasing alkaline oxides such as CaO and Al2O3, which begin to regulate the alkalinity of the surface furnace charge. When the temperature reaches 700-800℃, calcium carbonate decomposes and expands in volume by about 1.6 times. The high-pressure CO2 gas produced opens up deep pore channels, and the outer shell structure completely collapses, forming a porous and loose skeletal structure.

[0020] Through the above process, the porosity of the surface furnace charge increased from 30% to over 45%, and the air permeability resistance coefficient increased from 1200 Pa·s / m 3 Reduced to 750 Pa·s / m 3 The risk of surface crust formation is reduced, providing a smooth channel for subsequent gas escape.

[0021] As the charge continues to move downwards, the charge and the composite additives that have lost their outer shell enter the softening zone.

[0022] When the temperature reaches 800-1000℃, borax melts first and reacts with silicon powder and SiO2 in blast furnace slag to form a borosilicate glass phase, which adheres to the surface of soft slag particles and inhibits premature reduction of SiO2. When the temperature reaches 1000-1200℃, the CaO, MgO and CaF2 produced by the decomposition of dolomite form a low-melting-point eutectic, and the melting point drops to about 1120℃, and begins to gradually penetrate into the interior of high-viscosity slag. When the temperature reaches 1200-1400℃, the transition layer melts completely. The high viscosity manganese silicate in the slag undergoes a displacement reaction with CaF2 and MgO, destroying the silicon-oxygen tetrahedral network structure of the slag. The slag viscosity drops from 0.8 Pa·s to below 0.35 Pa·s, and the fluidity is significantly improved.

[0023] After the above process, the viscosity of slag in the softening layer decreases significantly, which can significantly reduce the slag clogging of the furnace charge pores, enable timely exhaust and heat dissipation, reduce the reaction rate caused by excessive local heating, and further promote gas generation, resulting in a sudden increase in pressure and causing sparking.

[0024] As the furnace charge continues to descend, the charge and core layer enter the main reaction zone above the molten pool. In this zone, the coke, silica, and manganese ore in the charge undergo a reduction reaction and enter the molten pool to form a silicon-manganese alloy. Due to the distribution of raw materials and temperature, the coke in this zone easily reacts with silicon to form a silicon carbide hard shell, hindering gas exhaust. In this application, the core layer uses activated coke as a framework, possessing abundant porosity to provide better gas flow channels. Simultaneously, the silicon carbide within the activated coke provides seed crystals for the silicon carbide formed by the reaction of coke and silicon. Since the silicon carbide in the core layer raw material is uniformly distributed, it acts as a seed crystal to induce the crystallization of newly formed silicon carbide on its surface, effectively reducing the disordered development of silicon carbide to form a large hard shell that blocks the gas flow channels. Through the above methods, combined with the gas permeability measures in the softening zone and the surface preheating zone, the large amount of carbon monoxide gas generated in the main reaction zone can be discharged in a timely manner, thereby significantly improving the problem of sparking caused by the sudden increase in pressure due to poor gas exhaust.

[0025] In a preferred embodiment, the mass content of CaO+MgO in the blast furnace slag is ≥45%; and the mass content of B2O3 in the borax is ≥35%.

[0026] The requirement that the CaO+MgO content of blast furnace slag be ≥45% is to allow it to act as a highly active alkaline flux component in the local micro-zone of the submerged arc furnace, so as to better regulate the slag performance and form a synergistic effect with the fluxing function of borax, thereby improving the problems of excessively high slag viscosity, pore blockage, and low MnO reduction efficiency that lead to sparking.

[0027] In a preferred embodiment, the activated coke in the core layer has a porosity ≥55% and a specific surface area ≥150 m².2 / g; the aluminum nitride content in the denitrified aluminum ash is ≤0.1% by mass.

[0028] In a preferred embodiment, the activated coke is prepared by heating coke to 500-600°C and pre-carbonizing it for 1-2 hours. Compared with ordinary coke, activated coke has more developed pores and a larger specific surface area, thus allowing for smoother gas flow during the reaction with silica or manganese ore powder, and resulting in more uniform mixing with manganese ore powder and silicon carbide.

[0029] In a preferred embodiment, the spherical particles have a particle size of 10-19 mm, wherein the core layer has a particle size of 5-8 mm, the transition layer has a coating thickness of 3-7 mm, and the outer shell has a coating thickness of 2-4 mm.

[0030] In a preferred embodiment, the composite additive contains P content ≤0.03% and S content ≤0.02% by mass.

[0031] A method for preparing a composite additive includes the following steps: The core layer raw materials are mixed evenly according to the formula, a binder is added, and the core particles are formed into 5-8 mm core particles by a disc granulator and then dried. A bottom-spray fluidized bed is used to coat the core particles with a transition layer. First, the transition layer powder is sprayed, and then the binder is atomized and sprayed in to coat the particles until the particle size is 8-15 mm. Lower the fluidized bed temperature, coat the outer shell layer in the same way as in the previous step until the final particle size is 10-19 mm, and then dry and solidify.

[0032] In a preferred embodiment, the operating air velocity of the fluidized bed is 1.2 to 1.8 m / s, and the spraying rate is 0.5 to 1 kg / min.

[0033] In a preferred embodiment, the curing process employs a gradient heating method with a heating rate of 5°C / min.

[0034] A method of using the above-mentioned three-layer coated additive includes the following steps: Weigh out 2% to 3% of the total mass of the charge in the electric arc furnace and add it to the mixer at the same time as the main materials of manganese ore, silica, coke, and flux. The mixed furnace charge is added to the electric arc furnace using a ring or multi-point feeding method; Adjust the proportion of composite additives according to the furnace conditions.

[0035] In a preferred embodiment, the particle size distribution of the main material is as follows: Manganese ore: ≥92% by mass of particles 10-50mm, and ≤8% by mass of other particle sizes; Silica: ≥97% of particles in the 10-60mm range by mass, and ≤3% of particles of other sizes by mass; Coke: 5-25mm particles account for ≥92% of the mass, and other particle sizes account for ≤8% of the mass; Flux: 5-40mm particles account for ≥88% of the mass, and other particle sizes account for ≤12% of the mass.

[0036] In normally operating submerged arc furnaces, over 90% of the charge reaction is uniform and stable, with only 5%–10% of localized defect areas prone to sparking. The composite additive in this application does not alter the reaction characteristics of all the charge, but rather acts on these 5%–10% defective areas. Therefore, only 2%–3% of the additive is needed to significantly improve the sparking problem in these defective areas. In other normal areas, the chemical and physical changes corresponding to the composite additive are also occurring. These normal areas have good venting and do not have sparking problems, but the additive can promote venting through pores, stabilizing the pressure in the space above the molten pool.

[0037] High-silicon ferromanganese alloys require continuous charge feeding during smelting to enable continuous production. The defect areas differ with each charge feeding. In actual production, different layers of material exhibit furnace charge permeability issues at different locations. This application addresses these issues by addressing each layer to improve the overall permeability of the furnace charge. For example, in the upper preheating layer, location A experiences permeability problems. The composite additive at location A expands and creates micropores, thus improving permeability. In the softening layer, location B suffers from slag viscosity clogging the permeable pores. The composite additive at location B reduces slag viscosity and improves its fluidity, effectively preventing slag blockage and improving permeability. In the main reaction zone, location C previously experienced blockage due to silicon carbide crust formation. The silicon carbide composition in the core layer of this application guides newly generated silicon carbide to crystallize using the core layer's silicon carbide as a seed crystal, preventing disordered crystallization and crust formation in this area, thereby improving permeability at location C. Thus, by incorporating composite additives into the furnace charge, this application can significantly improve the furnace charge permeability problem caused by factors such as charge distribution and batching, thereby improving the problem of sparking.

[0038] Composite additives are more expensive than ordinary furnace charge; excessive use of composite additives will increase operating costs. Furthermore, excessive amounts of highly active components in the core layer lead to excessively rapid gas production in the reaction zone, increasing furnace pressure fluctuations and consequently raising the risk of sparking. Excessive amounts of red mud, fluorite, and other components can cause the Al2O3 and CaF2 content in the slag to exceed threshold values, reducing slag fluidity and increasing residual manganese levels. Verification has shown that the composite additive used in this application should be used at 2%–3% of the total mass of the submerged arc furnace charge.

[0039] Another advantage of the composite additive in this application is that it effectively utilizes existing difficult-to-treat solid waste, including red mud and blast furnace slag. At the same time, the core silicon carbide can also be made from silicon carbide waste, which also effectively reduces production costs.

[0040] The present application will verify the solution through examples and comparative examples below.

[0041] This verification test was conducted on a 12500kVA enclosed submerged arc furnace for 10 days, with the baseline furnace conditions remaining consistent. Main raw material ratio: manganese ore 45%, coke 28%, silica 15%, lime 7%, dolomite 5% Baseline process parameters: secondary voltage 145V, electrode current 10500A, material layer height 1800mm, binary alkalinity 0.55~0.60.

[0042] Evaluation indicators: The number of times a flame is ignited per day is used as an indirect evaluation indicator of air permeability, while the manganese recovery rate is tested simultaneously.

[0043] Table 1 provides a description of the variables and formulations for the examples and comparative examples.

[0044] Table 1 Table 2 shows the test results for each embodiment and comparative example. Table 2: As shown in Tables 1 and 2, compared to the blank control group, the flame scorching reduction rate of Example 1, i.e., the fully coated additive of this application, reached 83.3%, which is much higher than the 46.0% of the mixed additive in Comparative Example 1. The reason is as follows: The coating structure enables the gradient release of components. The coating layer first acts as a fluxing and unblocking agent in the softening layer, and the core acts as an endothermic and rate-stabilizing agent in the high-temperature reaction layer, thus avoiding premature reaction and failure of mixed additive components. The coating layer's isolation function prevents the core active components from prematurely contacting and reacting with the furnace charge, significantly improving the utilization rate of functional components.

[0045] Comparative Example 2, using unmodified bentonite, had 2.6 more sparks than Example 1, and Comparative Example 3, using unactivated coke, had 2.2 more sparks than Example 1. This indicates that... Modified bentonite can more effectively improve surface permeability, and the surface furnace charge reaches its own layer during the downward movement, resulting in better permeability.

[0046] The porosity and specific surface area of ​​activated coke can significantly improve the permeability of the main reaction zone.

[0047] The number of spiking attempts increased to varying degrees after different components were missing from the coating layer, which demonstrates the necessity of the relevant component settings.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A composite additive for preparing high-silicon manganese alloys, having a spherical particle structure, characterized in that: From the inside out, it consists of a core layer, a transition layer, and an outer shell layer, with the following mass percentages for each layer: core layer 35%–45%, transition layer 30%–40%, and outer shell layer 20%–30%. The outer shell layer is composed of the following components in the indicated mass percentages: 50%–60% calcium carbonate, 20%–30% red mud, 10%–20% modified bentonite, and 3%–7% silica fume. The transition layer is composed of the following components in the indicated mass percentages: fluorite powder 30%–40%, dolomite 20%–30%, borax 10%–20%, blast furnace slag 15%–25%, and silica fume 3%–7%. The core layer is composed of the following components by mass percentage: 65%–75% activated coke, 15%–25% manganese ore powder, and 8%–12% silicon carbide.

2. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The red mud in the outer shell layer is calcined at 280-320℃, with a free alkali content of ≤0.5% and a pH value of ≤9.

3. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The modified bentonite is prepared through the following steps: Add 3-5% Na2CO3 to the bentonite slurry and stir and react at 60-80℃ for 30-60 minutes. Bentonite was aged at 80–100℃ under closed hydrothermal conditions for 12–24 hours. Heat the bentonite at 200–220℃ for 1–2 hours; then raise the temperature to 400–450℃ and calcine for 2–3 hours. Adding 0.5-1% silane coupling agent to bentonite can modify the surface of bentonite.

4. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The blast furnace slag contains ≥45% CaO+MgO by mass; the borax contains ≥35% B2O3 by mass.

5. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The activated coke in the core layer has a porosity ≥55% and a specific surface area ≥150m². 2 / g.

6. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The composite additive has a particle size of 10-19 mm, wherein the core layer has a particle size of 5-8 mm, the transition layer has a coating thickness of 3-7 mm, and the outer shell has a coating thickness of 2-4 mm.

7. The composite additive for preparing high-silicon manganese alloys as described in claim 1, characterized in that: The composite additive contains P with a mass content of ≤0.03% and S with a mass content of ≤0.02%.

8. The method for preparing the composite additive according to any one of claims 1 to 7, characterized in that, Includes the following steps: The core layer raw materials are mixed evenly according to the formula, a binder is added, and the core particles are formed into 5-8 mm core particles by a disc granulator and then dried. A bottom-spray fluidized bed is used to coat the core particles with a transition layer. First, the transition layer powder is sprayed, and then the binder is atomized and sprayed in to coat the particles until the particle size is 8-15 mm. Lower the fluidized bed temperature, coat the outer shell layer in the same way as the previous step, until the final particle size is 10-19 mm, and then dry and solidify.

9. The method for preparing the composite additive as described in claim 8, characterized in that: The fluidized bed operating air velocity is 1.2–1.8 m / s, and the spraying rate is 0.5–1 kg / min.

10. The method for preparing the composite additive as described in claim 8, comprising the following steps: The curing process employs a gradient heating method with a heating rate of 5℃ / min.

11. The method of using the composite additive as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Weigh out 2% to 3% of the total mass of the charge in the electric arc furnace and add it to the mixer at the same time as the main materials of manganese ore, silica, coke, and flux. The mixed furnace charge is added to the electric arc furnace using a ring or multi-point feeding method; Adjust the proportion of composite additives according to the furnace conditions.

12. The method of using the composite additive as described in claim 11, characterized in that, The particle size distribution of the main material is as follows: Manganese ore: ≥92% by mass of particles 10-50mm, and ≤8% by mass of other particle sizes; Silica: ≥97% of particles in the 10-60mm range by mass, and ≤3% of particles of other sizes by mass; Coke: 5-25mm particles account for ≥92% of the mass, and other particle sizes account for ≤8% of the mass; Flux: 5-40mm particles account for ≥88% of the mass, and other particle sizes account for ≤12% of the mass.

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